The present invention relates to a hand propelled projectile, particularly one that is longitudinally axial and more particularly one that is internally driven by the tip of the thrower's index finger within the volume defined by the outer casing of the projectile. The projectile is hand propelled because it is intended to be thrown by hand. It is internally driven because it is propelled from within the volume defined by the outer casing of the projectile, by the party throwing the projectile, particularly by his finger and more particularly by the tip of his index finger. The projectile is longitudinal axial because it rotates around its longitudinal axis. It is gyroscopic because the stability of its flight relies on gyroscopic action caused by the longitudinal axial rotation of the projectile after it is thrown. Although the type of projectile to which the invention is applied is not restricted, the most usual application for the invention is a throwing knife. Hereafter, a throwing knife will be discussed, but other projectiles adapted to the features of the invention are contemplated as well.
To throw a knife to hit a target situated on a plane, the person throwing the knife may use any of three known methods:
1. The thrower holds the knife blade at a point near its tip when throwing it. With reference to drawing FIG. 1 hereof, the knife travels through the air, spinning about its axis YY', or about another axis within the plane ZY, and the axis of spin passes through the center of gravity of the knife. For a thrown knife, the center of gravity flies through a parabolic pathway within the plane ZX. PA1 2. Instead of holding the blade by the tip, the thrower can hold the knife by its handle. With the knife thrown as described above, it is movable in virtually the same way as the first throwing method. PA1 3. Alternatively, the thrower can rest the knife on the palm of his hand with the point facing forward and can throw the knife with a sliding motion of the hand. The knife is propelled by rotation of the thrower's arm which accelerates the knife through centrifugal force. It is intended that the knife travel through the air like an airplane, with the tip of the blade substantially not wavering from pointing toward the target. However, if there is a deviation between the longitudinal axis of the knife and the velocity vector of the center of gravity, this produces a disturbing torque which exaggerates the deviation and renders the trajectory of the projectile unstable, which reduces the throwing range.
Spears and darts are examples of hand held projectiles which travel through the air with a forward facing tip, that is without revolving about an axis within the plane ZY. The sharp metal tips of both these types of projectile remain pointed toward the target because their center of gravity is in the sharp ended half of the projectile. As a result, the momentum of the force produced by deviation between the knife axis and the velocity of vector of the center of gravity is corrected, tending to align the axis with the velocity vector.
At least three types of hand held projectiles use gyroscopic spin to stabilize their flight. The first type includes spinning discs, such as those used as throwing toys, e.g. plastic spinning discs that are thrown at the beach, or spinning weapons known as Ninja stars. There is stability of the plane of the disc in flight because of the gyroscopic effect of the rotation of the disc. The kinetic momentum vector forms an angle of approximately 90.degree. with the velocity vector of the center of gravity. Therefore these are hand propelled transverse axial gyroscopic projectiles, rather than longitudinal axial projectiles.
The second type are boomerangs, which perform like the discs just discussed with respect to the angle between the kinetic momentum and the velocity of the center of gravity. However, the lack of symmetry of the object and its airplane wing-like profile produce a unique flight path.
Yet another example are spinning balls like rugby balls, which, to the inventor, appear to travel spinning through the air about a longitudinal axis with one end always pointing to the target. The players' fingers or body act on the outer surface of the ball to provide the drive end spin.
Returning to the knives thrown by holding either the tip or holding the handle, the thrown knife rotates about an axis which is perpendicular to the longitudinal axis, that is within the plane ZY. Because the knife is rotating, its point is directed at the target during each revolution for only a fraction of a second. For the knife tip to hit the target, the precise instant of the knife pointing at the target must coincide with the time when the knife point reaches the target, a coordination that is quite difficult to achieve. In the third case where the knife is thrown point forward by centrifugal force, while the knife tip is intended to point continuously at the target, this is difficult to achieve as such motion caused by throwing is mechanically unstable.